docs: def form_valid(self, post_form, attachment_formset, **kwargs):
          """ Processes valid forms.
  
          Called if all forms are valid. Creates a Post instance along with associated attachments if
          required and then redirects to a success page.
  
          """
          save_attachment_formset = attachment_formset is not None \
              and not self.preview
  
          if self.preview:
              return self.render_to_response(
                  self.get_context_data(
                      preview=True, post_form=post_form, attachment_formset=attachment_formset,
                      **kwargs
                  ),
              )
  
          # This is not a preview ; the object is going to be saved
          self.forum_post = post_form.save()
  
          if save_attachment_formset:
              attachment_formset.post = self.forum_post
              attachment_formset.save()
  
          messages.success(self.request, self.success_message)
          if not self.forum_post.approved:
              messages.warning(self.request, self.approval_required_message)
  
          return HttpResponseRedirect(self.get_success_url())